Routine Boiler Maintenance & Inspection5th Class Power Engineering Book 1, Unit 3 Chapter 12

Learning Outcome

Describe the service and maintenance required for boilers. Discuss the procedure for preparing a boiler for inspection and cleaning, and describe mechanical boiler cleaning methods

Glossary

• Combustion gases

• Rattler

• Soot blower

• Tags

Objective 1Describe the general servicing and routine maintenance of packaged firetube and cast-iron sectional boilers

Packaged Firetube Boiler Maintenance

• General maintenance• Watch for leaks in steam, water, fuel connections

• Tension on front and rear door closing bolts

• Feedwater pump packing glands

Door Bolts

Packaged Firetube Boiler Maintenance

• Lubrication• Blower motors

• Large valves have grease nipples to keep stems lubricated

• Gas valves

Packaged Firetube Boiler Maintenance

• Cleaning a new boiler• Take offline, shut down, drain, open, flush

• After first three months of operation

• Then annually unless more often warranted

Packaged Firetube Boiler Maintenance

• Cleaning the fireside• Open front and rear doors according to manufacturers instructions

• Remove flame retarders from tubes if used

• Brush soot, combustion debris

• Reinstall flame retarders if used

• Close doors according to manufacturers instructions

https://www.youtube.com/watch?v=bwuFEZBsxSA

https://www.youtube.com/watch?v=bwuFEZBsxSA

Packaged Firetube Boiler Refractory Maintenance

Packaged Firetube Boiler Maintenance

• Burner Maintenance • Observe flame in operation

• Remove burner for inspection, clean of soot/build-up

• Gas/oil fitter to set up annually using combustion analyser

Cast-iron Sectional Maintenance—Steam

• Steam boilers waterside drained, opened, cleaned• Gauge glass, piping, washout plugs, low water cut-off bodies

• Clean fireside• Soot, carbon is corrosive over the summer

• Re-assemble and leave full of water or in dry condition• Add corrosion treatment chemical

Cast-iron Sectional Maintenance—Hot Water

• Hot water boilers—do not open waterside• Isolate, dismantle, clean low water cut off body

• Clean fireside

Objective 2Explain the importance of lay-ups and state the procedures to be followed for wet and dry boiler lay-ups

Dry Lay-up

• Boiler out of service for a prolonged period

https://www.suezwatertechnologies.com/handbook/handbook-industrial-water-treatment

https://www.suezwatertechnologies.com/handbook/handbook-industrial-water-treatment

Dry Lay-up

• Clean waterside and fireside

• Inspect boiler, make necessary repairs

• Dry boiler completely—absorbing material (slack lime, silica gel, activated alumina), or blower

• Close manhole and handholes

• Protect fireside from corrosion by coating with mineral oil; close dampers to keep fireside dry

• Keep boiler and surrounding tidy

Wet Method

• Boiler on standby, ready for service• Clean boiler

• Fill and fire to drive oxygen from water

• Add chemicals to adjust alkalinity and oxygen scavenger

• Once boiler cooled, fill completely and connect drum to vent line; half fill drum with treated water

• Coat fireside with mineral oil

• Check boiler water chemical at least monthly

Objective 3 Describe symptoms of a leaking firetube

Boiler Repairs

• Consult with Office of the Fire Commissioner

• http://www.firecomm.gov.mb.ca/itsm_steam_pressure.html

http://www.firecomm.gov.mb.ca/itsm_steam_pressure.html

Defective Firetubes

• Tube failure• Overheating

• Caused by excessive firing rate

• poor water circulation

• heavy scale on the tubes (poor heat transfer)

• a low water condition

• Corrosion

• Cracked tube ends

Defective Firetubes

• Indicated by leakage• Minor leaks cause staining on tubesheet

• Major leaks cause water dripping from front or rear door

• Hissing sound at front or rear door

• Steam in the chimney (billowy white/black smoke)

Tube Attachment

Cracks in tube ends/tube sheet

• Develop over time

• Can seal under heat, open when boiler cools

• Hot/cool cycle speeds crack growth

Leak

• Shut down boiler firing immediately

• Close steam stop valve

• Close hot water stop and return valves

• Maintain normal water level/pressure

• Open front/rear doors and look

Cracks in tube ends/tube sheet

• Non-destructive testing (NDE)• Dye-penetrant

• Developer highlights crack

• Black Light• Penetrant under UV lights

Objective 4 List the steps and precautions to be taken to prepare a boiler for inspection

Annual certification inspection—OFC

• Steam boilers—internal

• Hot water boilers—operational/external

Internal Inspection

• Take boiler off line, cool, open vent

• Drain, flush

• Lockout-tagout (tagged valves) all sources of energy• Steam

• Water

• Electrical

• Take pumps/auxiliaries offline

• Open boiler waterside

• Open boiler fireside

• 12 V lighting; grounded & waterproof fixtures, ground extension cords, grounded

• PPE, confined space procedures

Internal Inspection

Open manholes

Internal Inspection

Internal Inspection

Flush tubes

Objective 5 Describe the inspection of a boiler

Inspections

• External (Operational)• Hot water boilers

• Internal• Waterside

• Fireside

Internal Fireside Inspection

• Cracking, corrosion, erosion, leakage• Tubesheet

• Fireside of tubes

• Furnace tube/firebox

• Refractory

• Indications of combustion performance

Internal Waterside Inspection

• Boiler drums

• Drum internals

• Tubes/tube connections

• Fittings (LWCO, connecting piping)

• Stays

• Manhole/handhole flange condition

• Scale, corrosion, pitting, cracking, indications of chemical treatment

Furnace Stays

Through or longitudinal

Diagonal

Staybolts

Firetubes

Firebox Boiler/Firetube Boiler Stays

Objective 6

• Describe methods and tools used for mechanical and chemical cleaning of a boiler

Boiler Cleaning

• Mechanical• “rattler”—air-driven hammer put through firetube boiler tubes to hammer

scale off the waterside

• Air or water driven brushes & cutting heads for waterside of watertubeboilers

• Wire brush for fireside of firetube “punch” tubes

Chemical Cleaning

• Alkaline boil out of new boiler to eliminate grease/oil• Caustic soda (sodium hydroxide/NaOH)

• Soda ash (Sodium Carbonate/Na2CO3)

• Sodium phosphate (Na2PO4)

• Sodium nitrite (NaNO2)

• Sodium sulphite (Na2So3)

• Raise and maintain pressure for 48 hours

• Inhibited Acid Cleaning• 5% hydrochloric acid

• 65C/150F

• Circulation Method

• Soak method

Boiler Cleaning

• Inhibited Acid• Dilute (5%), inhibited HCl or other acid/chealants

• Depending on constituents in deposit

• Non-ferrous parts protected

• Proper venting—H2 gas formed

• PPE, WHMIS, disposal

• Proper neutralization afterward cleaning

Inhibited Acid Cleaning

• Circulating Method• 65C (150F)

• Soak Method• 65C (150F)

Objective 7

• Discuss the standard procedure for a hydrostatic test and the reasons for doing the test

Hydrostatic Test

• Check for tightness of the pressure vessel• Always after weld repair

• Confirm suspected leak

Why “hydro”

• Water is non compressible

• If the pressure vessel fails during test, water will leak out at same volume at atmospheric pressure as it is at test pressure

• If a compressible gas (air, nitrogen) were to be used, and the pressure vessel fails, the gas volume would increase quickly (explosively) as it dropped from test pressure to atmospheric pressure

Hydrostatic test pressure

• 1.5 x MAWP as stamped on boiler

Procedure

• Close boiler except for vent and feedwater

• Isolate/remove gauge glass and controls that cannot withstand 1.5 x MAWP

• Remove safety valves (or gag)

• Fill completely with ambient temperature water (overflow the vent, then close vent)

• Use pump to raise to test pressure

• Hold test for 24 hours

• Bleed pressure slowly after test

Hydrostatic Pump

Sootblower

• An in-boiler device used to blow accumulated soot or ash off tubes and heating surfaces